1. Field of the Invention
This invention relates to electronic signal conditioning; and more specifically to control circuits for "blanking" the effects of noise radiated and electronically coupled by high voltage switching circuits.
2. Description of Related Art
Often, in applications involving structural and acoustic control of mechanical devices, amplifiers operating as Class-D types (switching), are used to drive active load elements, which, in turn, apply mechanical forces to the mechanical devices to be controlled. An example of one such amplifier is shown in U.S. Pat. No. 4,628,275.
It is also common in these applications to have a filter preceding the load containing an inductor for filtering purposes. As the output circuit turns the load current on and off, the inductor resists the change in current, creating a transient voltage spike, which is radiated through the air and through various parts of the circuit, housing, chassis and, importantly, over the ground line.
The problems associated with transient voltages ("noise") are particularly serious in pulse-width modulated (PWM) circuitry which employ level-comparing techniques to derive operating signals. In such systems, transient voltages are fed back, becoming error signals which are confused with the desired signals.
Error signals can occur timewise such that they create unwanted extra pulses actually inside a desired PWM pulse or trailing a PWM pulse. The unwanted extra pulses within desired PWM pulses can be eliminated, or severely reduced, with a low-pass filter where the additional signal delay is acceptable. Error signals which cause unwanted extra pulses trailing ("after") the desired PWM pulse are more difficult to eliminate, and must be dealt with by conventional EMI reduction methods, which are often very costly.